As this kind of work clamping device, a device which is provided with a plurality of reference pins extending in an up-and-down direction on an upper surface of a plate-like receiving member which is made of a ferromagnetic material and which presses and clamps a work toward the plate-like receiving member after positioning the work with regard to the plate-like receiving member in the horizontal direction by inserting the reference pins into positioning holes provided on a bottom surface of the work is known. (See PTL 1, for example.)
This work clamping device conducts clamping by a clamp mechanism after attracting a plurality of spacer seats made of a magnet to a voluntary position on the plate-like receiving member before inserting the reference pins into the positioning holes, positioning the work by the reference pins in a horizontal direction, and adjusting distance between the upper surface of the plate-like member and the lower surface of the work by the spacer seat.